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5.1

CHAPTER 5

REFRIGERANT SYSTEM CHEMISTRYRefrigerants ..................................................................................................................................... 5.1Chemical Reactions......................................................................................................................... 5.4Compatibility of Materials .............................................................................................................. 5.8Chemical Evaluation Techniques.................................................................................................. 5.10Refrigerant Database and ARTI/MCLR Research Projects.......................................................... 5.11

OOD understanding of the chemical interactions between re-Gfrigerant, lubricant, and materials in a refrigeration system isnecessary for designing reliable systems that have a long servicelife. This chapter covers the chemical aspects of both historicalrefrigerants and newer refrigerants and blends. Physical aspectssuch as measurement and contaminant control (including moisture)are discussed in Chapter 6. Physical properties of lubricants are dis-cussed in Chapter 7.

REFRIGERANTS

Environmental AcceptabilityCommon chlorine-containing refrigerants contribute to deple-

tion of the ozone layer. A material’s ozone depletion potential(ODP) is a measure of its ability, compared to CFC-11, to destroystratospheric ozone.

Halocarbon refrigerants also can contribute to global warmingand are considered greenhouse gases. The global warming poten-tial (GWP) of a greenhouse gas is an index describing its ability,compared to CO2 (which has a very long atmospheric lifespan), totrap radiant energy. The GWP, therefore, is connected to a particulartime scale (e.g., 100 or 500 years). For regulatory purposes, the con-vention is to use the 100-year integrated time horizon (ITH).

Appliances using a given refrigerant also consume energy, whichindirectly produces CO2 emissions that contribute to global warm-ing; this indirect effect is frequently much larger than the refriger-ant’s direct effect. An appliance’s total equivalent warmingimpact (TEWI) is based on the refrigerant’s direct warming poten-tial and indirect effect of the appliance’s energy use The life cycleclimate performance (LCCP), which includes the TEWI as well ascradle-to-grave considerations such as the climate change effect ofmanufacturing the refrigerant, transportation-related energy, andend-of-life disposal, is becoming more prevalent.

Environmentally preferred refrigerants (1) have low or zeroODP, (2) provide good system efficiency, and (3) have low GWP orTEWI values. Hydrogen-containing compounds such as the hydro-chlorofluorocarbon HCFC-22 or the hydrofluorocarbon HFC-134ahave shorter atmospheric lifetimes than chlorofluorocarbons(CFCs) because they are largely destroyed in the lower atmosphereby reactions with OH radicals, resulting in lower ODP and GWPvalues.

Tables 1 and 2 show boiling points, atmospheric lifetimes, ODPs,GWPs, and flammabilities of new refrigerants and the refrigerantsbeing replaced. ODP values were established through the MontrealProtocol and are unlikely to change. ODP values calculated usingthe latest scientific information are sometimes lower but are notused for regulatory purposes. Because HFCs do not contain chlorineatoms, their ODP values are essentially zero (Ravishankara et al.1994).

GWP values were established as a reference point using Inter-governmental Panel on Climate Change (IPCC 1995) assessmentvalues, as shown in Table 1, and are the official numbers used forreporting and compliance purposes to meet requirements of theUnited Nations Framework Convention on Climate Change(UNFCCC) and Kyoto Protocol. However, lifetimes and GWPshave since been reviewed (IPCC 2001) and are shown in Table 2,representing the most recent published values based on an updatedassessment of the science. These values are subject to review andmay change with future reassessments, but are currently not usedfor regulatory compliance purposes. Table 3 shows bubble pointsand calculated ODPs and GWPs for refrigerant blends, using thelatest scientific assessment values.

Compositional GroupsChlorofluorocarbons. CFC refrigerants such as R-12, R-11,

R-114, and R-115 have been used extensively in the air-condition-ing and refrigeration industries. Because of their chlorine content,these materials have significant ODP values. The Montreal Proto-col, which governs the elimination of ozone-depleting substances,was strengthened at the London meeting in 1990 and confirmed atthe Copenhagen meeting in 1992. In accordance with this interna-tional agreement, production of CFCs in industrialized countrieswas totally phased out as of January 1, 1996. Production in devel-oping countries will be phased out in 2010, although many havealready made considerable phaseout progress.

Hydrochlorofluorocarbons. HCFC refrigerants such as R-22and R-123 have shorter atmospheric lifetimes (and lower ODPvalues) than CFCs. Nevertheless, the Montreal Protocol limiteddeveloped-country consumption of HCFCs beginning January 1,1996, using a cap equal to 2.8% of the 1989 ODP weighted con-sumption of CFCs plus the 1989 ODP-weighted consumption ofHCFCs. The CAP was reduced by 35% by January 1, 2004, andwill be reduced by 65% on January 1, 2010; 90% by January 1,2015; 99.5% by January 1, 2020; and total phaseout by January 1,2030. From 2020 to 2030, HCFCs may only be used to serviceexisting equipment. Developing countries must freeze HCFCODP consumption at 2015 levels in 2016, and completely phaseout by January 1, 2040.

In addition to the requirements of the Montreal Protocol, severalcountries have established their own regulations on HCFC phaseoutof HCFCs. The United States has met the Montreal Protocol’srequirements by banning consumption of R-141b (primarily used asa foam-blowing agent) on January 1, 2003, and phasing out HCFC-142b (primarily foams) and HCFC-22 for original equipment man-ufacturers (OEMs) beginning January 1, 2010. Production for ser-vice needs is allowed to continue. Production and consumption ofall other HCFCs will be frozen on January 1, 2015. On January 1,2020, production and consumption of R-22 and R-142b will bebanned, followed by a ban on production and consumption of allother HCFCs on January 1, 2030. As required by the Montreal Pro-tocol, from 2020 to 2030, virgin HCFCs may only be used to serviceexisting equipment.

The preparation of this chapter is assigned to TC 3.2, Refrigerant SystemChemistry.

5.2 2006 ASHRAE Handbook—Refrigeration

Table 1 Refrigerant Properties: Regulatory Compliance Values Used by Governments for UNFCCC Reporting and Kyoto Protocol Compliance

Refrigerant StructureBoiling Point,a

°FAtmospheric Lifetime,b

Years ODPcGWP,

ITH 100-Year Flammable?

E125 CHF2OC F3 –43.6 165a 15,300a NoE143 CHF2OCH2F 85.8d YesE143a CF3OCH3 –11.4 5.7a 5400a Yes11 CC13F 74.7 50 1 4600a No12 CCl2F2 –21.6 102 1 10,600a No22 CHClF2 –41.4 12.1 0.055 1900a No23 CHF3 –115.8 264 11,700 No32 CH2F2 –61.1 5.6 650 Yes113 CCl2FCClF2 117.7 85 0.8 6000a No114 CClF2CClF2 38.5 300 1 9800a No115 CClF2CF3 –38.0 1700 0.6 10,300a No116 CF3CF3 –108.8 10,000 11,400a No123 CHCl2CF3 82.0 1.4 0.02 120a No124 CHClFCF3 10.4 6.1 0.022 620a No125 CHF2CF3 –54.6 32.6 2800 No134a CH2FCF3 –16.0 14.6 1300 No142b CClF2CH3 15.8 18.4 0.065 2300a Yes143 CH2FCHF2 41.0 3.8 300 Yes143a CF3CH3 –53.0 48.3 3800 Yes152a CHF2CH3 –11.2 1.5 140 Yes218 CF3CF2CF3 –33.9 2600a 8600a No227ea CF3CHFCF3 3.9 36.5 2900 No236ea CF3CHFCHF2 43.7d 10d 9400a No236fa CF3CH2CF3 29.5 209 6300 No245ca CHF2CF2CH2F –13.2 6.6 560 Yes245fa CF3CH2CHF2 59.2 8.8a 820a No

aData from Calm and Hourahan (1999).bData from IPCC (1995).

cData from Montreal Protocol (2003).dData from Chapter 5 of the 2002 ASHRAE Handbook—Refrigeration.

Table 2 Refrigerant Properties: Current IPCC Scientific Assessment Values

Refrigerant StructureBoiling Point,

°FAtmospheric Lifetime,

Years ODPGWP,

ITHa 100-Year Flammable?b

E125 CHF2OCF3 –43.6 165c 14,900 NoE143 CHF2OCH2F 85.1b 57 YesE143a CF3OCH3 –11.4 5.7c 750 Yes11 CHl3F 74.7 50 1 4600 No12 CCl2F2 –21.6 102 1 10,600 No22 CHClF2 –41.4 12.1 0.055 1700 No23 CHF3 –115.8 264 12,000 No32 CH2F2 –61.1 5.6 550 Yes113 CCl2FCF2Cl 117.7 85 0.8 6000 No114 CClF2CClF2 38.5 300 1 9800 No115 ClF2CF3 –38.0 1700 0.6 7200 No116 CF3CF3 –108.8 10,000 11,900c No123 CHCl2CF3 82.0 1.4 0.02 120 No124 CHClFCF3 10.4 6.1 0.022 620 No125 CHF2CF3 –54.6 32.6 3400 No134a CH2FCF3 –15.0 14.6 1300 No142b CH3CClF2 15.8 18.4 0.065 2400 Yes143 CH2FCHF2 41.0 3.8 330 Yes143a CH3CF3 –53.0 48.3 4300 Yes152a CH3CHF2 –11.2 1.5 120 Yes218 CF3CF2CF3 –33.9 2600c 8600c No227ea CF3CHFCF3 3.9 36.5 3500 No236ea CF3CHFCHF2 43.7b 10b 1200 No236fa CF3CH2CF3 29.5 209 9400 No245ca CHF2CF2CH2F 77.2 6.6 640 Yes245fa CF3CH2CHF2 59.2 8.8c 950 No

aData from IPCC (2001). bData from ASHRAE Standard 34. cData from Calm and Hourahan (1999).

Refrigerant System Chemistry 5.3

The European Union has already reduced the consumption capon HCFCs and accelerated the phase-out schedule. E.U. consump-tion of HCFCs was reduced 15% on January 1, 2002, by 55% onJanuary 1, 2003, and by 70% on January 1, 2004; future reductionsare to be by 75% on January 1, 2008, and total phaseout on January1, 2010. They also implemented several use restrictions on HCFCsin air-conditioning and refrigeration equipment.

U.S. and E.U. phaseout schedules allow continued, limited man-ufacture for developing-country needs or for export to other coun-tries where HCFCs are still legally used.

Atmospheric studies (Calm et al. 1999; Wuebbles and Calm1997) suggest that phaseout of HCFC refrigerants, with low atmo-spheric lives, low ozone depletion potentials, low global warmingpotentials, low emissions, and high thermodynamic efficiencies,will result in an increase in global warming, but have a negligibleeffect on ozone depletion.

HCFC-22 is the most widely used hydrochlorofluorocarbon.R-410A is now the leading alternative for HCFC-22 for new equip-ment. R-407C is another HCFC-22 replacement and can be used inretrofits as well as in new equipment. HCFC-123 is used commer-cially in large chillers.

Hydrofluorocarbons. These refrigerants contain no chlorineatoms, so their ODP is zero. HFC methanes, ethanes, and propaneshave been extensively considered for use in air conditioning andrefrigeration.

Fluoromethanes. Mixtures that include R-32 (difluoromethane,CH2F2) are being promoted as a replacement for R-22 and R-502.For very-low-temperature applications, R-23 (trifluoromethane,CHF3) has been used as a replacement for R-13 and R-503 (Atwoodand Zheng 1991).

Fluoroethanes. Refrigerant 134a (CF3CH2F) of the fluoroethaneseries is used extensively as a direct replacement for R-12 and as areplacement for R-22 in higher-temperature applications. R-125 andR-143a are used in azeotropes or zeotropic blends with R-32 and/orR-134a as replacements for R-22 or R-502. R-152a is flammableand less efficient than R-134a in applications using suction-line heatexchangers (Sandvordenker 1992), but it is still being considered forR-12 replacement. R-152a is also being considered as a component,with R-22 and R-124, in zeotropic blends (Bateman et al. 1990;Bivens et al. 1989) that can be R-12 and R-500 alternatives.

Fluoropropanes. Desmarteau et al. (1991) identified a number offluoropropanes as potential refrigerants. R-245ca is being consid-ered as a chlorine-free replacement for R-11. Evaluation by Doerret al. (1992) showed that R-245ca is stable and compatible with keycomponents of the hermetic system. However, Smith et al. (1993)demonstrated that R-245ca is slightly flammable in humid air atroom temperature. Keuper et al. (1996) investigated R-245ca per-formance in a centrifugal chiller; they found that the refrigerantmight be useful in new equipment but posed some problems whenused as a retrofit for R-11 and R-123 machines. R-245fa is used asa chlorine-free replacement for R-11 and R-141b in foams, and isbeing considered as a refrigerant and commercialized in organicRankine-cycle and waste-heat-recovery systems. R-236fa has beencommercialized as a replacement for R-114 in naval centrifugalchillers.

Fluoroethers. Booth (1937), Eiseman (1968), Kopko (1989),O’Neill (1992), O’Neill and Holdsworth (1990), and Wang et al.(1991) proposed these compounds as refrigerants. Fluoroethers areusually more physiologically and chemically reactive than fluori-nated hydrocarbons. Fluorinated ethers have been used as anesthet-ics and convulsants (Krantz and Rudo 1966; Terrell et al. 1971a,1971b). Reactivity with glass is characteristic of some fluoroethers(Doerr et al. 1993; Gross 1990; Simons et al. 1977). Misaki andSekiya (1995, 1996) investigated 1-methoxyperfluoropropane(boiling point 93.6°F) and 2-methoxyperfluoropropane (boilingpoint 84.9°F) as potential low-pressure refrigerants. Bivens andMinor (1997) reviewed the status of fluoroethers currently underconsideration and concluded that none appear to have a balance ofrefrigerant fluid requirements to challenge the HFCs.

Hydrocarbons. Hydrocarbons such as propane, n-butane(R-600), isobutane (R-600a), and blends of these are being used asrefrigerants. Hydrocarbons have zero ODP and low GWP. How-ever, they are very flammable, which is a serious obstacle to theirwidespread use as refrigerants. Hydrocarbons are commonly usedin small proportions in mixtures with nonflammable halogenatedrefrigerants and in small equipment requiring low refrigerantcharges. Hydrocarbons are currently used in air-conditioning andrefrigeration equipment in Europe and China (Lohbeck 1996;Mianmiam 1996; Powell 1996).

Ammonia. Used extensively in large, open-type compressors forindustrial and commercial applications, ammonia (R-717) has highrefrigerating capacity per unit displacement, low pressure losses inconnecting piping, and low reactivity with refrigeration lubricants(mineral oils). See Chapter 3 for detailed information.

The toxicity and flammability of ammonia offset its advantages.Ammonia is such a strong irritant to the human nose (detectable be-low 5 ppm) that people automatically avoid exposure to it. Ammo-nia is considered toxic at 35 to 50 ppm. Ammonia/air mixtures are

Table 3 Properties of Refrigerant Blendsa

Refrig-erant Composition

Bubble Point,b

°F ODPc

GWP,d

100-Year ITH

401A (22/152a/124)/(53/13/34) –27.9 0.027 1100401B (22/152a/124)/(61/11/28) –30.8 0.028 1200401C (22/152a/124)/(33/15/52) –19.1 0.025 900402A (125/C3H8/22)/(60/2/38) –56.2 0.013 2700402B (125/C3H8/22)/(38/2/60) –52.6 0.020 2300403A (C2H6/22/218)/(5/75/20) –54.0 0.026 3000403B (C2H6/22/218)/(5/56/39) –56.6 0.019 4300404A (125/143a/134a)/(44/52/4) –51.2 0 3800405A (22/152a/142b/C318)/(45/7/5.5/42.5) –27.2 0.018 5200406A (22/600a/142b)/(55/4/41) –26.9 0.036 1900407A 32/125/134a)/(20/40/40) –49.5 0 2000407B (32/125/134a)/(10/70/20) –52.2 0 2700407C (32/125/134a)/(23/25/52) –46.5 0 1700407D (32/125/134a)/(15/15/70) –39.1 0 1500407E (32/125/134a)/(25/15/60) –45.2 0 1400408A (125/143a/22)/(7/46/47) –48.3 0.016 3000409A (22/124/142b)/(60/25/15) –30.5 0.039 1500409B (22/124/142b)/(65/25/10) –32.1410A (32/125)/(50/50) –60.5 0 2000411A (R-1270/22/152a)/(1.5/87.5/11.0) –39.1 0.030 1500411B (1270/22/152a)/(3/94/3) –42.9 0.032 1600412A (22/218/142b)/(70/5/25) –36.4 0.035 2200413A (218/134a/600a)/(9/88/3) –23.1 0 1900414A (22/124/600a/142b)/(51/28.5/4/16.5) –29.2 0.032 1400414B (22/124/600a/142b)/(50/39/1.5/9.5) –27.2 0.031 1300415A (22/152a)/(82/18) –35.5 0.028 1400415B (22/152a)/(25/75) –17.9 0.009 500416A (134a/124/600)/(59/39.5/1.5) –10.1 0.010 1000417A (125/134a/600)/(46.6/50/3.4) –36.4 0.000 2200418A (290/22/152a)/(1.5/96/2.5) –42.2 0.33 1600500 (12/152a)/(73.8/26.2) –28.5 0.605 7900502 (22/115)/(48.8/51.2) –49.4 0.221 4500503 23/13/(40.1/59.9) –127.8 0.599 13,000507A (125/143a)/(50/50) –52.1 0 3900508A (23/116)/(39/61) –125.3 0 12,000508B (23/116)/(46/54) –124.6 0 12,000509A (22/218)/(44/56) –57.6 0.015 5600aData from IPCC (2001).bData from ARI Standard 700.cData from Calm (2001).dGWPs are weight fraction average for GWP values of individual components.


flammable, but only within a narrow range of 15.2 to 27.4% by vol-ume. These mixtures can explode but are difficult to ignite becausethey require an ignition source of at least 1200°F.

Carbon Dioxide. Some governments are promoting use of CO2in refrigeration and air-conditioning cycles. Trial cascade systemsare being used in Europe, and some countries in the European Unionare promoting transcritical carbon dioxide systems to replace HFC-134a in automotive air-conditioning systems. Higher costs areexpected because of the higher pressures and transcritical cycle.

Refrigerant AnalysisWith the introduction of many new pure refrigerants and refrig-

erant mixtures, interest in refrigerant analysis has increased. Refrig-erant analysis is addressed in ARI Standards 700 and 700c. Gaschromatographic methods are available to determine purity deter-mination of R-134a and R-141b (Gehring et al. 1992a, 1992b).Gehring (1995) discusses measurement of water in refrigerantsBruno and Caciari (1994) and Bruno et al. (1995) have done exten-sive work developing chromatographic methods for analysis ofrefrigerants using a graphitized carbon black column with a coatingof hexafluoropropene. Bruno et al. (1994) also published refractiveindices for some alternative refrigerants. There is interest in devel-oping methods for field analysis of refrigerant systems. Systems forfield analysis of both oils and refrigerants are commercially avail-able. Rohatgi et al. (2001) compared ion chromatography to otheranalytical methods for determining chloride, fluoride, and acids inrefrigerants. They also investigated sample vessel surfaces and lin-ers for absorption of hydrochloric and oleic acids.

Flammability and CombustibilityRefrigerant flammability testing is defined in UL Standard 2182,

Section 7. For many refrigerants, flammability is enhanced byincreased temperature and humidity. These factors must be con-trolled accurately to obtain reproducible, reliable data.

Fedorko et al. (1987) studied the flammability envelope of R-22/air as a function of pressure (up to 200 psia) and fuel (R-22)-to-oxygen ratio. They found that R-22 was nonflammable under75 psia. In addition, the flammable compositions between 30 and45% generated maximum heats of reaction. Their results were ingeneral agreement with those of Sand and Andrjeski (1982), whofound that pressurized mixtures of R-22 and at least 50% air arecombustible. R-11 and R-12 did not ignite under similar conditions.

Lindley (1992) and Reed and Rizzo (1991), using different ex-perimental arrangements, studied R-134a’s combustibility at hightemperature and pressure. Lindley notes that the results depend onthe equipment used. Reed and Rizzo showed that R-134a is combus-tible above 15 psig at room temperature and air concentrationsgreater than 80% by volume. At 350°F, combustibility was observedat pressures above 5 psig and air concentrations above 60% byvolume. Lindley found flammability limits of 8 to 22% by volume inair at 340°F and 100 psia. Both researchers found R-134a to be

nonflammable at ambient conditions and under the likely operatingconditions of air-conditioning and refrigeration equipment. Blendsof R-22/152a/114 combusted above 180°F at atmospheric pressureand above, with air concentrations above 80% by volume (Reed andRizzo 1991).

Richard and Shankland (1991) followed ASTM Standard E681’smethod to study flammability of R-32, R-141b, R-142b, R-152a,R-152, R-143, R-161, methylene chloride, 1,1,1-trichloroethane,propane, pentane, dimethyl ether, and ammonia. They used severalignition methods, including the electrically activated match ignitionsource specified in ASHRAE Standard 34. They also reported onthe critical flammability ratio of mixtures such as R-32/125,R-143a/134a, R-152a/125, propane/R-125, R-152a/22, R-152a/124, and R-152a/134a. The critical flammability ratio is the maxi-mum amount of flammable component that a mixture can containand still be nonflammable, regardless of the amount of air. Thesedata are important because mixtures containing flammable compo-nents are being considered as refrigerants.

Zhigang et al. (1992) published data on flammability ofR-152a/22 mixtures. Their measured lower flammability limit inair of R-152a is 11.4% by volume, though values reported in theliterature range from 4.7 to 16.8% by volume. Richard and Shank-land (1991) reported an average flammable range of 4.1 to 20.2%by mass for R-152a. Zhigang et al. (1992) also provide data onflame length as a function of R-22 concentration. They found thatthe flame no longer existed somewhere between 17 and 40% R-22by mass in the mixture. This is in apparent disagreement withRichard and Shankland’s (1991) data, which showed a criticalflammability ratio of 57.1% R-22 by mass. Comparison is diffi-cult because results depend on the apparatus and methods used.Grob (1991), reporting on flammabilities of R-152a, R-141b, andR-142b, describes R-152a as having “the lowest flammable mix-ture percentage, highest explosive pressure and highest potentialfor ignition of the refrigerants studied.” Womeldorf and Grosshan-dler (1995) used an opposed-flow burner to evaluate flammabilitylimits of refrigerants.

CHEMICAL REACTIONS

HalocarbonsThermal Stability in the Presence of Metals. All common

halocarbon refrigerants have excellent thermal stability, as shown inTable 4. Bier et al. (1990) studied R-12, R-134a, and R-152a. ForR-134a in contact with metals, traces of hydrogen fluoride (HF)were detected after 10 days at 392°F. This decomposition did notincrease much with time. R-152a showed traces of HF at 356°F afterfive days in a steel container. Bier et al. suggested that vinyl fluorideforms during thermal decomposition of R-152a, and can then reactwith water to form acetaldehyde. Hansen and Finsen (1992) con-ducted lifetime tests on small hermetic compressors with a ternarymixture of R-22/152a/124 and an alkyl benzene lubricant. In agree-

Table 4 Inherent Thermal Stability of Halocarbon Refrigerants

Refrigerant Formula

Decomposition Ratedat 400°F in Steel,

% per yra

Temperature at Which Decomposition Readily

Observed in Laboratory,b °F

Temperature at Which 1%/Year Decomposes in Absenceof Active Materials, °F

Major Gaseous Decomposition

Productsc

22 CHClF2 — 800 480 CF2CF2,d HCl

11 CCl3F 2 1100 570e R-12, Cl2114 CClF2CClF2 1 1100 710 R-12

115 CClF2CF3 — 1160 740 R-13

12 CCl2F2 Less than 1 1400 930 R-13, Cl213 CClF3 — 1550 1000f R-14, Cl2, R-116

Sources: Borchardt (1975), DuPont (1959, 1969), and Norton (1957).aData from UL Standard 207.bDecomposition rate is about 1% per min.cData from Borchardt (1975).

dVarious side products are also produced, here and with the other refrigerants, some of which may bequite toxic.

eConditions were not found where this reaction proceeds homogeneously.fRate behavior too complex to permit extrapolation to 1% per year.


ment with Bier et al., they found that vinyl fluoride and acetalde-hyde formed in the compressor. Aluminum, copper, and brass andsolder joints lower the temperature at which decomposition begins.Decomposition also increases with time.

Under extreme conditions, such as above red heat or with moltenmetal temperatures, refrigerants react exothermically to producemetal halides and carbon. Extreme temperatures may occur indevices such as centrifugal compressors if the impeller rubs againstthe housing when the system malfunctions. Using R-12 as the testrefrigerant, Eiseman (1963) found that aluminum was most reac-tive, followed by iron and stainless steel. Copper is relatively unre-active. Using aluminum as the reactive metal, Eiseman reported thatR-14 causes the most vigorous reaction, followed by R-22, R-12,R-114, R-11, and R-113. Dekleva et al. (1993) studied the reactionof various CFCs, HCFCs, and HFCs in vapor tubes at very high tem-peratures in the presence of various catalysts and measured theonset temperature of decomposition. These data also showed HFCsto be more thermally stable than CFCs and HCFCs, and that, whenmolten aluminum is in contact with R-134a, a layer of unreactivealuminum fluoride forms and inhibits further reaction.

Hydrolysis. Halogenated refrigerants are susceptible to reactionwith water (hydrolysis), but the rates of reaction are so slow thatthey are negligible (Table 5). Desiccants (see Chapter 6) are used tokeep refrigeration systems dry. Cohen (1993) investigated compat-ibilities of desiccants with R-134a and refrigerant blends.

AmmoniaReactions involving ammonia, oxygen, oil degradation acids,

and moisture are common factors in the formation of ammonia com-pressor deposits. Sedgwick (1966) suggested that ammonia orammonium hydroxide reacts with organic acids produced by oxida-tion of the compressor oil to form ammonium salts (soaps), whichcan decompose further to form amides (sludge) and water. The reac-tion is as follows:

Water may be consumed or released during the reaction, depend-ing on system temperature, metallic catalysts, and pH (acidic orbasic). Compressor deposits can be minimized by keeping the sys-tem clean and dry, preventing entry of air, and maintaining propercompressor temperatures. Ensure that ester lubricants and ammoniaare not used together, because large quantities of soaps and sludgeswould be produced.

At atmospheric pressure, ammonia starts to dissociate into nitro-gen and hydrogen at about 570°F in the presence of active catalystssuch as nickel and iron. However, because these high temperaturesare unlikely to occur in open-type compression systems, thermalstability is not a problem. Ammonia attacks copper in the presenceof even small amounts of moisture; therefore, except for some spe-cialty bronzes, copper-bearing materials and copper plating areexcluded in ammonia systems. (See the section on Copper Platingfor more information.)

LubricantsLubricants now in use and under consideration for new refriger-

ants are mineral oils, alkyl benzenes, polyol esters, polyalkyleneglycols, modified polyalkylene glycols, and polyvinyl ethers. Gun-derson and Hart (1962) give an excellent introduction to syntheticlubricants, including polyglycols and esters.

Polyol Esters. Commercial esters (Jolley 1991) are manufac-tured from four types of alcohols; (1) neopentyl glycol (NPG), withtwo OH reaction sites; (2) glycerin (GLY), with three OH sites;(3) trimethylolpropane (TMP) with three OH sites; and (4) pen-taerythritol (PER), with four OH sites. Formulas for the four alco-hol types are shown in Figure 1. Viscosities of the esters formed byreaction of a given acid with each of the four alcohol types are givenin Table 6.

Polyol esters are widely used as lubricants in HCFC refrigerantsystems, mainly because of their physical properties. Because theyare made from a wide variety of materials, polyol esters can bedesigned to optimize desired physical characteristics. The systemchemistry of the lubricant can be significantly influenced by the typeand chain length of the carboxylic acid used to prepare the ester.

Table 7 gives R-134a miscibility and viscosity data for severalesters based on pentaerythritol. Clearly, polyol ester lubricants rap-idly lose refrigerant miscibility when linear carbon chain lengthsexceed six carbons. Using branched chain acids to prepare theselubricants can greatly enhance refrigerant miscibility. Chain branch-ing also enables preparation of higher-viscosity esters, which areneeded in some industrial refrigeration applications.

Table 5 Rate of Hydrolysis in Water(Grams per Litre of Water per Year)

Refrig-erant Formula

14.7 psi at 86°FSaturation

Pressure at 122°F with SteelWater Alone With Steel

113 CCl2FCClF2 <0.005 50 4011 CCl3F <0.005 10 2812 CCl2F2 <0.005 1 1021 CHCl2F <0.01 5 9114 CClF2-CClF <0.005 1 322 CHClF2 <0.01 0.1 —

Source: DuPont (1959, 1969).

NH3 RCOOH+ RCOONH4 RCONH2⇔ ⇔ H2O+

Table 6 Influence of Type of Alcohol on Ester Viscosity

Type of AlcoholEster Viscosity at 104°F,

centistokes

Neopentyl glycol (NPG) 13.3Glycerin (GLY) 31.9Trimethylolpropane (TMP) 51.7Pentaerythritol (PER) 115

Note: Ester derived using the same carboxylic acid.

Table 7 R-134a Miscibility and Viscosity of Several Pentaerythritol-Based Esters

Acid UsedR-134a Miscibility at 20% Ester, °F

Ester Viscosity at 104°F, centistokes

5 carbon, linear <–94 15.66 carbon, linear –53 18.57 carbon, linear 34 21.28 carbon, linear >149 26.79 carbon, linear >149 31.05 carbon, branched <–94 25.28 carbon, branched 5 44.49 carbon, branched 17 112.9

Source: Jolley (1997).

Fig. 1 Types of Alcohols Used for Ester Synthesis

Fig. 1 Types of Alcohols Used for Ester Synthesis


The thermal stability of polyol esters is well known. Esters madefrom polyols that possess a central neo structure, which consists ofa carbon atom attached to four other carbon atoms (i.e., structurescorresponding to NPG, TMP, and PER in Figure 1), have outstand-ing thermal stability. Gunderson and Hart (1962) reviewed researchmeasuring the thermal stability of various polyol esters and dibasicacid esters at 500°F by heating them in evacuated tubes for up to250 h. These tests demonstrated the increased thermal stabilityexpected from neo ester structures, with dibasic acid esters decom-posing three times faster than the polyol esters.

Hydrolysis of Esters. An alcohol and an organic acid react toproduce an organic ester and water; this reaction is called esterifi-cation, and it is reversible. The reverse reaction of an ester and waterto produce an alcohol and an organic acid is called hydrolysis:

Hydrolysis may be the most important chemical stability issueassociated with esters. The degree to which esters are subject tohydrolysis is related to their processing parameters [particularlytotal acid number (TAN), degree of esterification, nature of the cat-alyst used during production, and catalyst level remaining in thepolyol ester after processing] and their structure. Dick et al. (1996)demonstrated that (1) using polyol esters prepared with acids knownas α-branched acids significantly reduces ester hydrolysis and(2) using α-branched esters with certain additives can eliminatehydrolysis.

Hydrolysis is undesirable in refrigeration systems because freecarboxylic acid can react with and corrode metal surfaces. Metalcarboxylate soaps that may be produced by hydrolysis can alsoblock capillary tubes. Davis et al. (1996) reported that polyol esterhydrolysis proceeds through autocatalytic reaction, and determinedreaction rate constants for hydrolysis using sealed-tube tests. Jolleyet al. (1996) and others used compressor testing, along with varia-tions of the ASHRAE Standard 97 sealed-tube test, to examine thepotential for lubricant hydrolysis in operating systems. Compressortests run with lubricant saturated with water (2000 ppm) have gone2000 h with no significant capillary tube blockage, indicating thatunder normal, much drier operating conditions, little or no detri-mental ester hydrolysis occurs with use of polyol ester lubricants.Hansen and Snitkjær (1991) demonstrated ester hydrolysis in com-pressor life tests run without desiccants and in sealed tubes. Theydetected hydrolysis by measuring the total acid number and showedthat desiccants can reduce the extent of hydrolysis in a compressor.They concluded that, with filter-driers, refrigeration systems usingesters and R-134a can be very reliable.

Greig (1992) ran the thermal and oxidation stability test (TOST)by heating an oil/water emulsion to 203°F and bubbling oxygenthrough it in the presence of steel and copper. Appropriate additivescan suppress hydrolysis of esters. Although agreeing that esters canbe used in refrigeration, Jolley et al. (1996) point out that some addi-tives are themselves subject to hydrolysis. Cottington and Ravner(1969) and Jones et al. (1969) studied the effect of tricresyl phos-phate, a common antiwear agent, on ester decomposition.

Field and Henderson (1998) studied the effect of elevated levelsof organic acids and moisture on corrosion of metals in the presenceof R-134a and POE lubricant. Copper, brass, and aluminum showedlittle corrosion, but cast iron and steel were severely corroded. At392°F, iron caused the POE lubricant to break down, even in theabsence of additional acid and moisture. Similar chemistry wasreported by Klauss et al. (1970), who found that high-temperature(600°F) decomposition of POE was catalyzed by iron. Naidu et al.(1988) showed that this POE/iron reaction did not occur at a mea-surable rate at 365°F. Cottington and Ravner (1969) reported thatthe presence of TCP inhibits the POE/iron reaction, which Lilje(2000) concluded is a high-energy process and does not occur in

properly operating refrigeration systems. Field lubricant analysisdata, after 5 years of operation, support this conclusion: no lubricantdegradation was observed (Riemer and Hansen 1996).

Polyalkylene Glycols (PAGs). Polyalkylene glycols are of thegeneral formula RO—[CH2—CHR′—O]—R′. They are used aslubricants in automotive applications that use R-134a. Linear PAGscan have one or two terminal hydroxyl groups. Modified PAG mol-ecules have both ends capped by various groups. Sundaresan andFinkenstadt (1990) discuss the use of PAGs and modified PAGs inrefrigeration compressors. Short and Cavestri (1992) present dataon PAGs.

These lubricants and their additive packages may (1) oxidize, (2)degrade thermally, (3) react with system contaminants such aswater, and/or (4) react with refrigerant or system materials such aspolyester films.

Oxidation is usually not a problem in hermetic systems usinghydrocarbon oils, because no oxygen is available to react with thelubricant. However, if a system is not adequately evacuated or if airis allowed to leak into the system, organic acids and sludges can beformed. Clark et al. (1985) and Lockwood and Klaus (1981) foundthat iron and copper catalyze the oxidative degradation of esters.These reaction products are detrimental to the refrigeration systemand can cause failure. Komatsuzaki et al. (1991) have suggested thatthe oxidative breakdown products of PAG lubricants and perhaps ofesters are volatile, whereas those of mineral oils are more likely toinclude sludges.

Sanvordenker (1991) studied thermal stability of PAG and esterlubricants and found that, above 400°F, water is one of the decom-position products of esters (in the presence of steel) and of PAGlubricants. He recommends that polyol esters be used with metalpassivators to enhance their stability when in contact with metallicbearing surfaces, which can experience 400°F temperatures. San-vordenker presents data on the kinetics of the thermal decomposi-tion of polyol esters and PAGs. These reactions are catalyzed bymetal surfaces in the following order: low carbon steel > aluminum> copper (Naidu et al. 1988).

Lubricant AdditivesAdditives are often used to improve lubricant performance in

refrigeration systems, and have become more important as use ofHFC refrigerants has increased. Chlorine in CFC refrigerants actedas an antiwear agent, so mineral-oil lubricants needed minimal or noadditives to provide wear protection. HFC refrigerants such asR-134a do not contain chlorine and thus do not provide this antiwearbenefit. Additives such as antioxidants, detergents, dispersants, rustinhibitors, etc., are not normally used because the conditions theytreat are absent from most refrigeration systems. Many HFC/polyolester refrigeration systems function well without lubricant addi-tives. However, some systems that have aluminum wear surfacesrequire an additive to supplement wear protection. Antiwear protec-tion is likely to be necessary in future systems with lower-viscositylubricants to improve energy efficiency, especially if branched-acidpolyol esters are used. Randles et al. (1996) discuss the advantagesand disadvantages of using additives in polyol ester lubricants forrefrigeration systems.

The active ingredient in antiwear additives is typically phos-phorous, sulfur, or both. Organic phosphates, phosphites, and phos-phonates are typical phosphorous-containing antiwear agents.Tricresylphosphate (TCP) is the best known of these. Sulfurizedolefins and disulfides are typical of sulfur-containing additives forwear protection. Zinc dithiophosphates are the best examples ofmixed additives. Vinci and Dick (1995) showed that additives con-taining phosphorous can perform well as antiwear agents, and thatsulfur-containing additives are not thermally stable as determinedby the ASHRAE Standard 97 sealed-tube stability test.

Other additives used in HFC/polyol ester combinations arefoam-producing agents (compressor start-up noise reduction) and

RCOOR′

EsterHOHWater

+ RCOOHAcid

⇔ R′OHAlcohol

+


hydrolysis inhibitors. Vinci and Dick (1995) show that a combina-tion of antiwear additive and hydrolysis inhibitor can produceexceptional performance in both wear and capillary tube blockagein bench testing and long-term compressor endurance tests. San-vordenker (1991) has shown that iron surfaces can catalyze thedecomposition of esters at 400°F. He proposed using a metal passi-vator additive to minimize this effect in systems where high temper-atures are possible. Schmitz (1996) describes the use of a siloxaneester foaming agent for noise reduction. Swallow et al. (1995, 1996)suggested using additives to control the release of refrigerant vaporfrom polyol ester lubricants.

System ReactionsAverage strengths of carbon/chlorine, carbon/hydrogen, and

carbon/fluorine bonds are 78, 93, and 100 kcal/mole, respectively(Pauling 1960). The relative stabilities of refrigerants that containchlorine, hydrogen, and fluorine bonded to carbon can be under-stood by considering these bond strengths. The CFCs have charac-teristic reactions that depend largely on the presence of the C—Clbond. Spauschus and Doderer (1961) concluded that R-12 can reactwith a hydrocarbon oil by exchanging a chlorine for a hydrogen. Inthis reaction, characteristic of chlorine-containing refrigerants,R-12 forms the reduction product R-22, R-22 forms R-32 (Spaus-chus and Doderer 1964), and R-115 forms R-125 (Parmelee 1965).For R-123, Carrier (1989) demonstrated that the reduction productR-133a is formed at high temperatures.

Factor and Miranda (1991) studied the reaction between R-12,steel, and oil sludge. They concluded that it can proceed by a pre-dominantly Friedel-Crafts mechanism in which Fe3+ compounds arekey catalysts. They also concluded that oil sludge can be formed bya pathway that does not generate R-22. They suggest that, except forthe initial formation of Fe3+ salts, the free-radical mechanism playsonly a minor role. Further work is needed to clarify this mechanism.

Huttenlocher (1992) tested 23 refrigerant-lubricant combina-tions for stability in sealed glass tubes. HFC refrigerants wereshown to be very stable even at temperatures much higher than nor-mal operating temperatures. HCFC-124 and HCFC-142b wereslightly more reactive than the HFCs, but less reactive than CFC-12.HCFC-123 was less reactive than CFC-11 by a factor of approxi-mately 10.

Fluoroethers were studied as alternative refrigerants. Sealed-glass-tube and Parr bomb stability tests with E-245 (CF3—CH2—O—CHF2) showed evidence of an autocatalytic reaction with glassthat proceeds until either the glass or the fluoroether is consumed(Doerr et al. 1993). High pressures (about 2000 psi) usually causethe sealed glass tubes to explode.

Breakdown of CFCs and HCFCs can usually be tracked byobserving the concentration of reaction products formed. Alterna-tively, the amount of fluoride and chloride formed in the system canbe observed. For HFCs, no chloride will be formed, and reactionproducts are highly unlikely because the C—F bond is strong.Decomposition of HFCs is usually tracked by measuring the fluo-ride ion concentration in the system (Spauschus 1991; Thomas andPham 1989; Thomas et al. 1993); according to this test, R-125,R-32, R-143a, R-152a, and R-134a are quite stable.

The possibility that hydrogen fluoride released by the breakdownof the refrigerants being studied will react with glass of the sealedtube is a concern. Sanvordenker (1985) confirmed this possibilitywith R-12. Spauschus et al. (1992) found no evidence of fluoride onthe glass surface of sealed tubes with R-134a.

Figures 2 and 3 show sealed-tube test data for reaction rates ofR-22 and R-12 with oil in the presence of copper and mild steel. For-mation of chloride ion was taken as a measure of decomposition.These figures show the extent to which temperature acceleratesreactions, and that R-22 is much less reactive than R-12. The dataonly illustrate the chemical reactivities involved and do not repre-sent actual rates in refrigeration systems.

The chemistry in CFC systems retrofitted to use HFC refriger-ants and their lubricants is an area of growing interest. Corr et al.(1992) point out that a major problem is the effect of chlorinatedresidues in the new system. Komatsuzaki et al. (1991) showed thatR-12 and R-113 degrade PAG lubricants. Powers and Rosen(1992) performed sealed-tube tests and concluded that the thresh-old of reactivity for R-12 in R-134a and PAG lubricant is between1 and 3%.

Copper PlatingCopper plating is the formation of a copper film on steel surfaces

in refrigeration and air-conditioning compressors. A blush of cop-per is often discernible on compressor bearing and valve surfaceswhen machines are cut apart. After several hours of exposure to air,this thin film becomes invisible, probably because metallic copperis converted to copper oxide. In severe cases, the copper deposit canbuild up to substantial thickness and interfere with compressoroperation. Extreme copper plating can cause compressor failure.

Although the exact mechanism of copper plating is not com-pletely understood, early work by Spauschus (1963), Steinle andBosch (1955), and Steinle and Seeman (1951, 1953) demonstratedthat three distinct steps must occur: (1) copper oxidation, (2) solu-bilization and transport of copper ions, and (3) deposition of copperonto iron or steel.

In step 1, copper oxidizes from the metallic (0 valent) state toeither the +1 or +2 oxidation state. Under normal operating

Fig. 2 Stability of Refrigerant 22 Control System

Fig. 2 Stability of Refrigerant 22 Control System(Kvalnes and Parmelee 1957)

Fig. 3 Stability of Refrigerant 12 Control Systems

Fig. 3 Stability of Refrigerant 12 Control System(Kvalnes and Parmelee 1957)

LIVE GRAPHClick here to view


/knovel2/view_hotlink.jsp?hotlink_id=1500000761



conditions, this chemical process does not occur with a lubricant,and is unlikely to occur with carboxylic acids. The most likelysource of oxidizing agents is system contaminants, such as air(oxygen), chlorine-containing species (CFC refrigerants or clean-ing solvents, solder fluxes), or strong acids.

Step 2 is dissolution of the copper ions. Spauschus postulatedthat an organic complex of the copper and olefins is the soluble spe-cies in mineral oils. Oxygen-containing lubricants are much morelikely to solubilize metal ions and/or complexes via coordinationwith the oxygen atoms. Once soluble, the copper can move through-out the refrigeration system.

Step 3 is deposition of the copper onto iron surfaces, an electro-chemical process in which electrons transfer from iron to copper,resulting in copper metal (0 valent) plating on the surface of the ironand the concomitant generation of iron ions. This is more likely tooccur on hot, clean iron surfaces and is often seen on bearing sur-faces.

Thomas and Pham (1989) compared copper plating in R-12/mineral oil and R-134a/PAG systems. They showed that R-134a/PAG systems produced much less total copper (in solution and asprecipitate) than R-12/mineral oil systems, and that water did notsignificantly affect the amount of copper produced. In the R-134a/PAG system, copper was largely precipitated. In the R-12/mineraloil system, the copper was found in solution when dry and precipi-tated when wet. Walker et al. (1960) found that water below the sat-uration level had no significant effect on copper plating for R-12/mineral oil systems. Spauschus (1963) observed that copper platingin sealed glass tubes was more prevalent with medium-refinednaphthenic pale oil than with a highly refined white oil. He con-cluded that the refrigerant/lubricant reaction was an essential pre-cursor for gross copper plating. The excess acid produced byrefrigerant decomposition had little effect on copper solubility, butfacilitated plating. Herbe and Lundqvist (1996, 1997) examined alarge number of systems retrofitted from R-12 to R-134a for con-taminants and copper plating. They reported that copper platingdid not occur in retrofitted systems where the level of contaminantswas low.

Contaminant Generation by High TemperatureHermetic motors can overheat well beyond design levels under

adverse conditions such as line voltage fluctuations, brownouts, orinadequate airflow over the condenser coils. Under these condi-tions, motor winding temperatures can exceed 300°F. Prolongedexposure to these thermal excursions can damage motor insulation,depending on the insulation materials’ thermal stability and reactiv-ity with the refrigerant and lubricant, and the temperature levelsencountered.

Another potential for high temperatures is in the bearings. Oil-film temperatures in hydrodynamically lubricated journal bearingsare usually not much higher than the bulk oil temperature; however,in elastohydrodynamic films in bearings with a high slide/roll ratio,the temperature can be several hundred degrees above the bulk oiltemperature (Keping and Shizhu 1991). Local hot spots in boundarylubrication can reach very high temperatures, but fortunately, theamount of material exposed to these temperatures is usually verysmall. The appearance of methane or other small hydrocarbon mol-ecules in the refrigerant indicates lubricant cracking by high bearingtemperatures.

Thermal decomposition of organic insulation materials and sometypes of lubricants produces noncondensable gases such as carbondioxide and carbon monoxide. These gases circulate with the refrig-erant, increasing the discharge pressure and lowering unit effi-ciency. At the same time, compressor temperature and deteriorationrate of the insulation or lubricant increase. Liquid decompositionproducts circulate with the lubricating oil either in solution or as col-loidal suspensions. Dissolved and suspended decomposition prod-ucts circulate throughout the refrigeration system, where they clog

oil passages; interfere with operation of expansion, suction, and dis-charge valves; or plug capillary tubes.

Appropriate control mechanisms in the refrigeration system min-imize exposure to high temperatures. Identifying potential reac-tions, performing adequate laboratory tests to qualify materialsbefore field use, and finding means to remove contaminants gener-ated by high-temperature excursions are equally important (seeChapter 6).

COMPATIBILITY OF MATERIALS

Electrical InsulationInsulation on electric motors is affected by the refrigerant and/or

the lubricant in two main ways: extraction of insulation polymerinto the refrigerant or absorption of refrigerant by the polymer.

Extraction of insulation material causes embrittlement, delami-nation, and general degradation of the material. In addition, ex-tracted material can separate from solution, deposit out, and causecomponents to stick or passages (e.g., capillary tubes) to clog.

Refrigerant absorption can change the material’s dielectricstrength or physical integrity through softening or swelling. Rapiddesorption (off-gassing) of refrigerant caused by internal heatingcan be more serious, because it results in high internal pressures thatcause blistering or voids within the insulation, decreasing its dielec-tric or physical strength.

In compatibility studies of 10 refrigerants and 7 lubricants with24 motor materials in various combinations, Doerr and Kujak(1993) showed that R-123 was absorbed to the greatest extent, butR-22 caused more damage because of more rapid desorption andhigher internal pressures. They also observed insulation damageafter desorption of R-32, R-134, and R-152a in a 300°F oven, butnot as much as with R-22.

Compatibility studies of motor materials were also conductedunder retrofit conditions in which materials were exposed to theoriginal refrigerant/mineral oil followed by exposure to the alter-native refrigerant/polyolester lubricant (Doerr and Waite 1995,1996a). Alternative refrigerants included R-134a, R-407C, R-404A,and R-123. Most motor materials were unaffected, except forincreased brittleness in polyethylene terephthalate (PET) caused bymoisture and blistering between layers of sheet insulation from theadhesive. Many of the same materials were completely destroyedwhen exposed to ammonia; the magnet wire enamel was degraded,and the PET sheet insulation completely disappeared, having beenconverted to a terephthalic acid diamide precipitate (Doerr andWaite 1996b).

Ratanaphruks et al. (1996) determined the compatibility of met-als, desiccants, motor materials, plastics, and elastomers with theHFCs R-245ca, R-245fa, R-236ea, and R-236fa, and HFE-125. Mostmetals and desiccants were compatible. Plastics and elastomers werecompatible except for excessive absorption of refrigerant or lubricant(resulting in unacceptable swelling) observed with fluoropolymers,hydrogenated nitrile butyl rubber, and natural rubber. Corr et al.(1994) tested compatibility with R-22 and R-502 replacements.Kujak and Waite (1994) studied the effect on motor materials of HFCrefrigerants with polyol ester lubricants containing elevated levels ofmoisture and organic acids. They concluded that a 500 ppm moisturelevel in polyol ester lubricant had a greater effect on the motor mate-rials than an organic acid level of 2 mg KOH/g. Exposure to R-134a/polyol ester with a high moisture level had less effect than exposureto R-22/mineral oil with a low moisture level.

Ellis et al. (1996) developed an accelerated test to determine thelife of motor materials in alternative refrigerants using a simulatedstator unit. Hawley-Fedder (1996) studied breakdown products of asimulated motor burnout in HFC refrigerant atmospheres.

Magnet Wire Insulation. Magnet wire is coated with heat-curedenamels. The most common insulation is a polyester base coat fol-lowed by a polyamide imide top coat; a polyester imide base coat is


also used. Acrylic and polyvinyl formal enamels are found on oldermotors. An enameled wire with an outer layer of polyester-glass isused in larger hermetic motors for greater wire separation and ther-mal stability.

Magnet wire insulation is the primary source of electrical insu-lation and the most critical in compatibility with refrigerants. Mostelectrical tests (NEMA Standard MW 1000) are conducted in airand may not be valid for hermetic motors. For example, wire enam-els absorb R-22 up to 15 to 30% by mass (Hurtgen 1971) and at dif-ferent rates, depending on their chemical structure, degree of cure,and conditions of exposure to the refrigerant. Refrigerant perme-ation is shown by changes in electrical, mechanical, and physicalproperties of the wire enamels. Fellows et al. (1991) measureddielectric strength, Paschen curve minimum, dielectric constant,conductivity, and resistivity for 19 HFCs in order to predict electri-cal properties in the presence of these refrigerants.

Wire enamels in refrigerant vapor typically exhibit dielectric losswith increasing temperature, as shown in Figure 4. Depending onthe atmosphere and degree of cure, each wire enamel or enamel/var-nish combination exhibits a characteristic temperature tmax, abovewhich dielectric losses increase sharply. Table 8 shows values oftmax for several hermetic enamels. Continued heating above tmaxcauses aging, shown by the irreversible alteration of dielectric prop-erties and increased conductance of the insulating material.

Spauschus and Sellers (1969) showed that the change rate in con-ductance is a quantitative measure of aging in a refrigerant environ-ment. They proposed aging rates for varnished and unvarnishedenamels at two levels of R-22 pressure, typical of high- and low-sidehermetic motor operation.

Apart from the effects on long-term aging, R-22 can also affectthe short-term insulating properties of some wire enamels. Beachamand Divers (1955) demonstrated that polyvinyl formal’s resistancedrops drastically when it is submerged in liquid R-22. A parallel

experiment using R-12 showed a much smaller drop, followed byquick recovery to the original resistance. The relatively rapid per-meation of R-22 into polyvinyl formal, coupled with R-22’s lowvolume resistivity and other electrical properties of the two refrig-erants, explains the phenomenon.

With certain combinations of coatings and refrigerants, wirecoatings can soften, which can cause the insulation to fail. Table 9shows data on softening measured in terms of abrasion resistancefor a number of wire enamels exposed to R-22. At the end of theshortest soaking period, the urethane-modified polyvinyl formalhad lost all its abrasion resistance. All the other insulations, exceptpolyimide, lost abrasion resistance more slowly, approaching, overthree months, the rate of the urethane-polyvinyl formal. The poly-imide showed only a minimal effect, although its abrasion resis-tance was originally among the lowest.

Because of the time dependency of softening, which is related tothe rate of R-22 permeation into the enamel, Sanvordenker andLarime (1971) proposed that comparative tests on magnet wire bemade only after the enamel is completely saturated with refrigerant,so that the effect on enamel properties of long-term exposure toR-22 can be evaluated.

The second consequence of R-22 permeation is blistering,caused by the rapid change in pressure and temperature after a wireenamel is exposed to R-22. Heating greatly increases the internalpressure as the dissolved R-22 expands; because the polymer filmhas already been softened, portions of the enamel lift up in the formof blisters. Although blistered wire has a poor appearance, fieldexperience indicates that mild blistering is not cause for concern, aslong as the blisters do not break and the enamel film remains flexi-ble. Modern wire enamels have the characteristics mentioned pre-viously and maintain dielectric strength even after blistering.However, hermetic wire enamel with strong resistance is preferred.

Varnishes. After the stator of an electric motor is wound, it isusually treated with a varnish by a vacuum-and-pressure impregna-tion process for form-wound, high-voltage motors or a dip-and-bake process for low-voltage, random wound motors. The varnishedmotor is cured in a 275 to 350°F oven. The varnish holds the wind-ings together in the magnetic field and acts as a secondary source ofelectrical insulation. The windings have a tendency to move, andindependent movement of the wires abrades and wears the insula-tion. High-voltage motors contain form-wound coils wrapped witha porous fiberglass, which is saturated with varnish and cured as anadditional layer.

Many different chemicals are used as motor varnishes. The mostcommon are epoxies, polyesters, phenolics, and modified polyim-ides. Characteristics important to a varnish are good adhesion andbond strength to the wire enamel; flexibility and strength under bothheat and cold; thermal stability; good dielectric properties; andchemical compatibility with wire enamel, sheet insulation, andrefrigerant/lubricant mixture.

Table 8 Maximum Temperature tmax for Hermetic Wire Enamels in R-22 at 65 psia

Enamel Type tmax, °F

Acrylic 226Polyvinyl formal 277Isocyanate-modified polyvinyl formal 304Polyamide imide 361Polyester imide 419Polyimide 450

Fig. 4 Loss Curves of Various Insulating Materials

Fig. 4 Loss Curves of Various Insulating Materials(Spauschus and Sellers 1969)

Table 9 Effect of Liquid R-22 on Abrasion Resistance

Magnet Wire InsulationAs

Received

After Time in Liquid R-22

7 to 10 Days

One Month

Three Months

Urethane/polyvinyl formal batch 1

40 3 2 2

Urethane/polyvinyl formal batch 2

42 2 2 7

Polyester imide batch 1 44 15 18 6Polyester imide batch 2 24 10 5 6Dual-coat amide/imide top

coat, polyester base79 35 23 11

Dual-coat, polyester 35 5 5 9Polyimide 26 25 23 21

Source: Sanvordenker and Larime (1971).




Varnish compatibility is determined by exposing the cured var-nish (in the form of a section of a thin disk and varnished magnetwire in single strands, helical coils, and twisted pairs) to a refriger-ant at elevated temperatures. The varnish’s properties are then com-pared to samples not exposed to refrigerant and to other exposedsamples placed in a hot oven to rapidly remove absorbed refrigerant.Disk sections are evaluated for absorption, extraction, degradation,and changes in flexibility. The single strands are wound around amandrel, and the varnish is examined for flexibility and effect on thewire enamel. In many cases, the varnish does not flex as well as theenamel; if bound tightly to the enamel, the varnish removes it fromthe copper wire. The helical coils are evaluated for bond strength(ASTM Standard D2519) before and after exposure to a refriger-ant/lubricant mixture. The twisted pair is tested for dielectric break-down voltage, or burnout time, while subjected to resistance heating(ASTM Standard D1676).

During compatibility testing of motor materials with alternativerefrigerants, researchers observed that varnish can absorb consider-able amounts of refrigerant, especially R-123. Doerr (1992) studiedthe effects of time and temperature on absorption and desorptionrates of R-123 and R-11 by epoxy motor varnishes. Absorption wasfaster at higher temperatures. Desorption was slow at temperaturesas high as 250°F. The equilibrium absorption value for R-123 waslinearly dependent on temperature, with higher absorption at lowertemperatures. Absorption of R-11 remained the same at all test tem-peratures.

Ground Insulation. Sheet insulation material is used in slot lin-ers, phase insulation, and wedges in hermetic motors. The sheetmaterial is usually a PET film or an aramid (aromatic polyamide)mat, used singly or laminated together. PET or aramid films haveexcellent dielectric properties and good chemical resistance torefrigerants and oils.

The PET film selected must contain little of the low-relative-molecular-mass polymers that exhibit temperature-dependent solu-bility in mineral lubricants and tend to precipitate as noncohesivegranules at temperatures lower than those of the motor. Another lim-itation is that, like most polyesters, this film is susceptible to degra-dation by hydrolysis; however, the amount of water required is morethan that generally found in refrigerant systems. Sundaresan andFinkenstadt (1991) discuss the effect of synthetic lubricants on PETfilms. Dick and Malone (1996) reported that low-viscosity POEstend to extract more low-oligomeric PET components than higher-viscosity esters.

ElastomersRefrigerants, oils, or mixtures of both can, at times, extract

enough filler or plasticizer from an elastomer to change its physi-cal or chemical properties. This extracted material can harm therefrigeration system by increasing its chemical reactivity or byclogging screens and expansion devices. Many elastomers areunsuitable for use with refrigerants because of excessive swellingor shrinkage (e.g., some neoprenes tend to shrink in HFC refrig-erants, and nitriles swell in R-123). Hamed and Seiple (1993a,1993b) determined swell data on 95 elastomers in 10 refrigerantsand seven lubricants. Compatibility data on general classificationsof elastomers such as neoprenes or nitriles should be used withcaution because results depend on the particular formulation.Users should be aware that elastomeric behavior is stronglyaffected by the elastomer’s specific formulation as well as by itsgeneral type.

PlasticsThe effect of refrigerants on plastics usually decreases as the

amount of fluorine in the molecule increases. For example, R-12 hasless effect than R-11, whereas R-13 is almost entirely inert. Cavestri(1993) studied the compatibility of 23 engineering plastics withalternative refrigerants and lubricants.

Each type of plastic material should be tested for compatibilitywith the refrigerant before use. Two samples of the same type of plas-tic might be affected differently by the refrigerant because of differ-ences in polymer structure, relative molecular mass, and plasticizer.

CHEMICAL EVALUATION TECHNIQUES

Chemical problems can often be attributed to inadequate testing ofa new material, improper application of a previously tested material,or inadvertent introduction of contaminants into the system. Threetechniques are used to chemically evaluate materials: (1) sealed-tubematerial tests, (2) component tests, and (3) system tests.

Sealed-Tube Material TestsThe glass sealed-tube test, described in ASHRAE Standard 97, is

widely used to assess stability of refrigerant system materials and toidentify chemical reactions that are likely to occur in operatingunits.

Generally, glass tubes are charged with refrigerant, oil, metalstrips, and other materials to be tested, and then sealed and aged atelevated temperatures for a specified time. The tubes are inspectedfor color and appearance and compared to control tubes that are pro-cessed identically to the specimen tubes, but might contain a refer-ence material rather than the test material. Contents can be analyzedfor changes by gas, ion, or liquid chromatography; infrared spec-troscopy; specific ion electrode; or wet methods, such as total acidnumber analysis.

The sealed-tube test was originally designed to compare lubri-cants, but it is also effective in testing other materials. For example,Huttenlocher (1972) evaluated zinc die castings, Guy et al. (1992)reported on compatibilities of motor insulation materials and elas-tomers, and Mays (1962) studied R-22 decomposition in the pres-ence of 4A-type molecular sieve desiccants.

Although the sealed tube is very useful, it has some disadvan-tages. Because chemical reactions likely to occur in a refrigerationsystem are greatly magnified, results can be misinterpreted. Also,reactions in which mechanical energy plays a role (e.g., in a failingbearing) are not easily studied in a static sealed tube.

Despite its proven utility, the sealed-tube test is only a screeningtool and not a full simulation of a refrigeration system. Sealed-tubetests alone should not be used to predict field behavior. Materialselection for refrigerant systems requires follow-up with componentor system tests or both.

Component TestsComponent tests carry material evaluations a step beyond sealed-

tube tests: materials are tested not only in the proper environment,but also under dynamic conditions. Motorette (enameled wire,ground insulation, and other motor materials assembled into a sim-ulated motor) tests used to evaluate hermetic motor insulation, asdescribed in Underwriters Laboratories (UL) Standard 984, are agood example of this type of test. Component tests are conducted inlarge pressure vessels or autoclaves in the presence of a lubricantand a refrigerant. Unlike sealed-tube tests, in which temperature andpressure are the only means of accelerating aging, autoclave testscan include external stresses (e.g., mechanical vibration, on/offelectrical voltages, liquid refrigerant floodback) that may acceleratephenomena likely to occur in an operating system.

System TestsSystem tests can be divided into two major categories:

• Testing a sufficient number of systems under a broad spectrum ofoperating conditions to obtain a good, statistical reference base.Failure rates of units containing new materials can be comparedto those of units containing proven materials.

• Testing under well-controlled conditions. Temperatures, pres-sures, and other operating conditions are continuously monitored.


Refrigerant and lubricant are chemically analyzed before, during,and after the test.

In most cases, tests are conducted under severe operating condi-tions to obtain results quickly. Analyzing lubricant and refrigerantsamples during the test and inspecting the components after tear-down can yield information on the (1) nature and rate of chemicalreactions taking place in the system, (2) products formed by thesereactions, and (3) possible effects on system life and performance.Accurate interpretation of these data determines system operatinglimits that keep chemical reactions at an acceptable level.

REFRIGERANT DATABASE AND ARTI/MCLR RESEARCH PROJECTS

The U.S. Department of Energy (DOE) funded research throughthe Air-Conditioning and Refrigeration Technology Institute toaccelerate phaseout of CFCs and conversion to alternative refrig-erants and lubricants. The funds supported about 40 materialscompatibility and lubricants research (MCLR) projects and a refrig-erants database (Calm 2001).

The database covers over 5000 references with abstracts or sum-maries of presentations and technical papers. Performance, physicalproperty, toxicity, compatibility, and flammability data for refriger-ants are also included.

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ASHRAE. 1999. Sealed glass tube method to test the chemical stability ofmaterial for use within refrigerant systems. ANSI/ASHRAE Standard97-1999 (RA2003).

ASTM. 2003. Test methods for film-insulated magnet wire. ANSI/ASTMStandard D1676-03. American Society for Testing and Materials, WestConshohocken, PA.

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Atwood, T. and J. Zheng. 1991. Cascade refrigeration systems: The HFC-23solution. International CFC and Halon Alternatives Conference, Balti-more, MD, sponsored by The Alliance for Responsible CFC Policy,Arlington, VA, pp. 442-450.

Bateman, D.J., D.B. Bivens, R.A. Gorski, W.D. Wells, R.A. Lindstrom, R.A.Morse, and R.L. Shimon. 1990. Refrigerant blends for the automotive airconditioning aftermarket. SAE Technical Paper Series 900216. Societyof Automotive Engineers, Warrendale, PA.

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Calm, J.M. 2001. ARTI refrigerant database . Air-Conditioning and Refrig-eration Technology Institute, Arlington, VA.

Calm, J.M. and G.C. Hourahan. 1999. Physical, safety, and environmentaldata for refrigerants. HPAC Engineering (August).

Calm, J.M., D.J. Wuebbles, and A.K. Jain. 1999. Impacts of global ozoneand climate from use and emissions of 2,2-dichloro-1,1,1-trifluoroethane(HCFC-123). Journal of Climatic Change 42:439-474.

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Corr, S., R.D. Gregson, G. Tompsett, A.L. Savage, and J.A. Schukraft. 1992.Retrofitting large refrigeration systems with R-134a. Proceedings of theInternational Refrigeration Conference—Energy Efficiency and NewRefrigerants 1:221-230. Purdue University, West Lafayette, IN.

Corr, S., P. Dowdle, G. Tompsett, R. Yost, T. Dekleva, J. Allison, and R.Brutsch. 1994. Compatibility of non-metallic motor components withRH22 and R-502 replacements. ASHRAE Winter Meeting, NewOrleans, LA. ARTI refrigerant database 4216. Air-Conditioning andRefrigeration Technology Institute, Arlington, VA.

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Doerr, R.G., D. Lambert, R. Schafer, and D. Steinke. 1992. Stability andcompatibility studies of R-245ca, CHF2—CF2—CH2F, a potential low-pressure refrigerant. International CFC and Halon Alternatives Con-ference, Washington, D.C., pp. 147-152.

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Doerr, R.G., D. Lambert, R. Schafer, and D. Steinke. 1993. Stability studiesof E-245 fluoroether, CF3—CH2—O—CHF2. ASHRAE Transactions99(2):1137-1140.

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